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¹ Department of Physiology, Nagoya City University Medical School, Mizuho-ku, Nagoya 467-8601, Japan

The cellular mechanisms that determine the frequency of spontaneous activity were investigated in gastric smooth muscles isolated from the guinea-pig. Intact antral muscle generated slow waves periodically; the interval between slow waves was decreased exponentially by depolarization of the membrane to reach a steady interval value of about 7 s. Isolated circular muscle bundles produced slow potentials spontaneously or were evoked by depolarizing current stimuli. Evoked slow potentials appeared in an all-or-none fashion, with a refractory period of 2–3 s. Low concentrations of chemicals that modify intracellular signalling revealed that the refractory period was causally related to the activity of protein kinase C (PKC). Activation of PKC increased and inhibition of PKC activity decreased the frequency of slow potentials. Chemicals that inhibit mitochondrial functions reduced the frequency of slow waves. Inhibition of internal Ca²⁺-store activity decreased the amplitude, but not the frequency of slow potentials, suggesting that the amplitude is causally related to Ca²⁺ release from the internal store. The results suggest that changes in [Ca²⁺]_i caused by the activity of mitochondria may play a key role in determining the frequency of spontaneous activity in gastric pacemaker cells.

(Received 13 July 2006; accepted after revision 30 August 2006; first published online 31 August 2006)
Corresponding author H. Suzuki: Department of Physiology, Nagoya City University Medical School, Mizuho-ku, Nagoya 467-8601, Japan. Email: hisuzuki{at}med.nagoya-cu.ac.jp

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